What is Ammonium Dichromate Definition Formula Preparation Reactions and Uses
How Do You Define The Terminology Ammonium Dichromate(NH4)2Cr2O7?
Ammonium dichromate is an inorganic compound with the chemical formula (NH4)2Cr2O7. It is orange-red needles produced during crystallization.
Ammonium dichromate is a salt consisting of ammonium ions and dichromate ions, a toxic chemical salt used to sensitize organic emulsion. It is more sensitive to light. It is readily ignited and burns to leave a sizable green residue. If ammonium dichromate is heated in a closed container, it may rupture due to the decomposition of the material. It also acts as a reliable oxidizing agent mixed with or contaminated with combustible material.
The following figure highlights a few of the things about Ammonium dichromate:
Because of its application in demonstrations of tabletop "volcanoes", Ammonium dichromate is sometimes also termed as Vesuvian Fire. However, in schools, this demonstration became unpopular due to the compound's carcinogenic nature. It has also been used in pyrotechnics and the early days of photography.
A glimpse, let's have a look to the names of Ammonium dichromate:
IUPAC name – diammonium oxido-(oxido-dioxo-chromio) oxy-dioxo-chromium,
Other names – Ammonium bichromate
Ammonium pyrochromate, Chromic acid, diammonium salt; diammonium dichromate; Ammonium bichromate; Ammonium pyrochromate.
The following points and table give a depth-understanding of the various features or characteristics of Ammonium dichromate. These are as follows:
The density of ammonium dichromate is 2.12g/cm 3
It has a melting point of 180°c
Exact molecular mass - 251.924166
Ammonium dichromate is an explosive compound.
The action makes chromic acid on ammonium hydroxide with subsequent crystallization.
Features of Ammonium Dichromate
Ammonium Dichromate Structure – (NH4)2Cr2O7.
The Ammonium dichromate follows a particular pattern or structure. This can be seen as follows:
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Properties of Ammonium Dichromate
The properties of Ammonium dichromate are explained by dividing them into two main categories. These are:
Physical Properties.
Chemical Properties.
These will be explained one by one as follows:
Physical Properties of Ammonium Dichromate – (NH4)2Cr2O7
The physical properties of Ammonium dichromate are as follows:
It is orange-red crystals.
It is soluble in water and alcohol at room temperature.
Ammonium dichromate is odorless.
Other Properties Can Be Made More Transparent With The Help of The Following Chart
Chemical properties of Ammonium Dichromate-
At room temperature and pressure, it is orange, acidic crystal soluble in water and alcohol. On heating Ammonium dichromate, it undergoes decomposition, resulting in chromium (III) oxide and nitrogen gas formation.
(NH4)2Cr2O7(s) → Cr2O3(s) + N2 (g) + 4H2O (g).
Hazards and safety of Ammonium Dichromate -
Main hazards of ammonium dichromate are as follows:
Dangerous, very toxic, a carcinogen, mutagen, oxidizing, dangerous for the environment.
To deal with these hazards, one needs to follow safety measures. These includes:
Safety: Ammonium dichromate, like all chromium (VI) compounds, is highly toxic and is also explosive under certain conditions. It is also a strong irritant.
Safety measures need to be taken while using ammonium dichromate. Wear eye protection and avoid skin contact with ammonium dichromate (wear gloves).
Uses of Ammonium Dichromate – (NH4)2Cr2O7
Ammonium dichromate has various applications. These are explained as follows:
Ammonium dichromate is used in sensitizing solutions used in lithography.
They are used in pyrotechnics, lithography, and photoengraving. It is also used as a magnetic recording material.
It is used as an approved pesticide and used as a mordant for dyeing, used as a pigment.
It is also used as a mordant for dyeing pigments, in the manufacturing of alizarin, chrome alum, leather tanning, and oil purification.
Reactions: Ammonium dichromate depicts various reactions, and these include:
Oxidation Reactions
Ammonium dichromate acts as an oxidizing agent. Often reacts violently with any reducing agent: the more influential the reducing agent, the more violent the reaction. Even in the oxidation of aliphatic alcohols, the compound is being applied. This is being used for their corresponding aldehydes and ketones in ZrCl4/wet SiO2 in solvent-free conditions. This is done again with relatively high yields.
Reactions: Consisting of tabletop volcanoes and thermal decomposition.
If you add a few drops of ethanol to a small pile of ammonium dichromate and ignite, you will notice a spark will emit, and an ash-like product will form. This phenomenon resembles the eruption of a volcano.
FAQs on Ammonium Dichromate Structure Properties and Reactions
1. What is ammonium dichromate?
Ammonium dichromate is an inorganic compound with the chemical formula (NH4)2Cr2O7 that contains ammonium and dichromate ions. It consists of two NH4+ ions and one Cr2O72- ion.
- It is an orange crystalline solid.
- It is a strong oxidizing agent.
- It is best known for the “volcano experiment” due to its thermal decomposition.
2. What is the formula for ammonium dichromate?
The chemical formula for ammonium dichromate is (NH4)2Cr2O7. It is formed from:
- Two ammonium ions (NH4+)
- One dichromate ion (Cr2O72-)
3. What happens when ammonium dichromate is heated?
When heated, ammonium dichromate decomposes into chromium(III) oxide, nitrogen gas, and water vapor. The balanced thermal decomposition reaction is:
(NH4)2Cr2O7(s) → Cr2O3(s) + N2(g) + 4H2O(g)
- This reaction is highly exothermic.
- It produces green Cr2O3 ash.
- It is demonstrated in the classic ammonium dichromate volcano experiment.
4. Why is ammonium dichromate called the volcano experiment?
Ammonium dichromate is called the volcano experiment because its decomposition produces sparks, gases, and a growing pile of green ash resembling a volcanic eruption. During heating:
- Rapid release of N2 and H2O vapor causes expansion.
- Orange crystals convert to green Cr2O3.
- The reaction is strongly exothermic, sustaining the effect.
5. Is ammonium dichromate an oxidizing agent?
Yes, ammonium dichromate is a strong oxidizing agent because it contains chromium in the +6 oxidation state. In Cr2O72-, chromium is +6 and can be reduced to +3, as seen in:
(NH4)2Cr2O7(s) → Cr2O3(s)
- Cr is reduced from +6 to +3.
- Other substances are oxidized in redox reactions.
6. What is the oxidation state of chromium in ammonium dichromate?
The oxidation state of chromium in ammonium dichromate is +6. In the dichromate ion Cr2O72-:
- Oxygen is −2 each (7 × −2 = −14).
- Let oxidation state of 2 Cr = x.
- x − 14 = −2 → x = +12.
- Each Cr = +6.
7. How is ammonium dichromate prepared?
Ammonium dichromate is prepared by reacting ammonium salts with dichromic acid or by neutralizing chromic acid with ammonia. A common preparation method is:
2NH3(aq) + H2Cr2O7(aq) → (NH4)2Cr2O7(aq)
- The solution is evaporated to crystallize orange crystals.
- It must be handled carefully due to toxicity.
8. What are the uses of ammonium dichromate?
Ammonium dichromate is used mainly as an oxidizing agent and in laboratory demonstrations. Its key uses include:
- Demonstrating thermal decomposition (volcano experiment).
- As a photographic chemical in older processes.
- In pyrotechnics and safety matches (historically).
9. Is ammonium dichromate toxic or hazardous?
Yes, ammonium dichromate is highly toxic and contains carcinogenic chromium(VI). Major hazards include:
- Strong oxidizing properties.
- Skin and respiratory irritation.
- Environmental toxicity to aquatic life.
10. What type of reaction is the decomposition of ammonium dichromate?
The decomposition of ammonium dichromate is a thermal decomposition and redox reaction. In the reaction:
(NH4)2Cr2O7(s) → Cr2O3(s) + N2(g) + 4H2O(g)
- It is a decomposition reaction because one compound breaks into simpler substances.
- It is a redox reaction because Cr is reduced (+6 to +3) and nitrogen is oxidized (−3 to 0).
- It is strongly exothermic.
